JP2002298840A - Positive active material for alkaline storage battery and alkaline storage battery using the same - Google Patents

Abstract

(57) [Problem] To provide a positive electrode active material for an alkaline storage battery and an alkaline storage battery having excellent high-rate discharge characteristics while maintaining excellent high-temperature charge characteristics. SOLUTION: In solid solution particles containing nickel hydroxide as a main component, 1 to 30% of the surface area of the solid solution particles is coated with at least one oxide particle selected from yttrium, scandium or lanthanoid, and the outer periphery thereof Is coated with a cobalt oxide having an average cobalt valence of more than 3.0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode active material for an alkaline storage battery and an alkaline storage battery using the same.

[0002]

2. Description of the Related Art In recent years, there has been a strong demand for alkaline storage batteries to have higher capacities with the spread of portable devices. Especially nickel
A hydrogen storage battery is a secondary battery including a positive electrode mainly composed of nickel hydroxide and a negative electrode mainly composed of a hydrogen storage alloy.
It is widely used as a high capacity and highly reliable secondary battery.

Hereinafter, the positive electrode for an alkaline storage battery will be described.

The positive electrodes for alkaline storage batteries are roughly classified into two types: a sintered type and a non-sintered type. The former has a porosity of 80 obtained by sintering a core material such as punched metal and nickel powder.
% Nickel sintered substrate is impregnated with a nickel salt solution such as an aqueous solution of nickel nitrate, and then is impregnated with an aqueous alkali solution to produce nickel hydroxide in the porous nickel sintered substrate. is there. Since it is difficult for the positive electrode to further increase the porosity of the substrate, the amount of nickel hydroxide cannot be increased, and there is a limit to increasing the capacity.

As the latter non-sintered positive electrode, for example, as disclosed in JP-A-50-36935, a three-dimensionally continuous nickel foam substrate having a porosity of about 95% is used.
Those that hold nickel hydroxide particles have been proposed, and are currently widely used as positive electrodes of high-capacity alkaline storage batteries. In this non-sintered positive electrode, spherical nickel hydroxide particles having a large bulk density are used from the viewpoint of increasing the capacity. Further, in order to improve discharge characteristics, charge acceptability, and life characteristics, it is common to use a metal element such as cobalt, cadmium, or zinc in a solid solution in the above nickel hydroxide particles.

Further, as a conductive agent to be held on the foamed nickel substrate together with such nickel hydroxide particles, divalent cobalt oxide (for example, JP-A-7-77129) has been proposed.

The function of the divalent cobalt oxide is as follows. Usually, the size of the holes of the foamed nickel substrate is provided sufficiently larger than the particle size of the nickel hydroxide to be filled therein. Therefore, the charge / discharge reaction proceeds smoothly in the nickel hydroxide particles near the substrate skeleton where the current collection is maintained, but the reaction of the nickel hydroxide particles separated from the skeleton does not sufficiently proceed. Therefore, in many cases, divalent cobalt oxides such as cobalt hydroxide and cobalt monoxide are added. Although these divalent cobalt oxides have no conductivity per se, they are electrochemically oxidized into β-cobalt oxyhydroxide having conductivity during initial charging in a battery, and this is converted to nickel hydroxide particles. It functions as a conductive network connecting the substrate and the substrate skeleton. Due to the presence of the conductive network, the utilization rate of the active material filled at high density can be significantly increased in the non-sintered positive electrode, and the capacity can be increased as compared with the sintered positive electrode.

However, even in the non-sintered positive electrode having the above-described structure and the alkaline storage battery using the same, the current collection performance of the conductive network by cobalt is not perfect, so that the utilization rate of the nickel hydroxide particles is reduced. Had an upper limit.
Furthermore, in the above-described positive electrode, when the battery is left in an overdischarged or short-circuit state, or when stored for a long time or at a high temperature, etc.,
There was a disadvantage that the capacity of the positive electrode was reduced by subsequent charging and discharging. This is because, in the electrochemical cobalt oxidation reaction in the battery as described above, divalent cobalt oxide is completely converted to β.
-It is because it cannot be changed to cobalt oxyhydroxide and the function of the conductive network is likely to be reduced.

As means for improving the imperfectness of the conductive network due to such cobalt, Japanese Patent Application Laid-Open No. 8-14881 discloses a method.
No. 45 and JP-A-8-148146, heat treatment (oxidation) of cobalt hydroxide in a positive electrode active material in the presence of an alkaline aqueous solution and oxygen (air) outside a battery causes disordered crystal structure. A technique for modifying cobalt oxide having a valence larger than divalent is disclosed. As contents similar to this, an improvement of cobalt oxide having a cobalt valence of 2.5 to 2.93 in JP-A-9-147905 and a similar method in JP-A-9-259888 were produced. The characteristics of the battery using β-cobalt oxyhydroxide are shown.

The above-mentioned Japanese Patent Application Laid-Open No. 8-148146 also discloses that a similar heat treatment is applied to nickel hydroxide solid solution particles having a coating layer of cobalt hydroxide. In this case, there is an advantage that the amount of cobalt used can be reduced for reasons such as improvement in the dispersibility of cobalt by preparing cobalt hydroxide-coated nickel hydroxide solid solution particles in advance. On the other hand, JP-A-9-73
Japanese Patent Publication No. 900 discloses a method for producing a solid solution particle of a cobalt hydroxide-containing nickel hydroxide containing an aqueous alkaline solution in a fluidized-granulation apparatus or the like while heating or dispersing the solid-solution particles in the fluidized-granulation apparatus. I have. By performing such a process, there is an advantage that troubles such as generation of a particle mass due to aggregation can be reduced.

However, in the positive electrode active material for an alkaline storage battery (nickel hydroxide solid solution particles having a coating layer of an oxidized cobalt species) described in the above publication, the oxidation state of the cobalt species forming the coating layer is still incomplete. Hard to say
There was room for improvement. This is because the progress of oxidation of cobalt hydroxide in the presence of alkali is greatly affected not only by the ambient temperature and the concentration of the aqueous alkaline solution to coexist, but also by the amount of ambient moisture and oxygen, and without these controls. This is because it cannot be oxidized to a sufficiently high-order state. As a proposal for improving this problem, Japanese Patent Application Laid-Open No. H11-97
No. 008, the cobalt species forming the coating layer by optimally controlling the oxidation conditions have a valence of 3.0.
The point that it is oxidized to higher γ-cobalt oxyhydroxide than that, and the utilization rate and overdischarge resistance of the positive electrode using this active material, when using an active material with insufficient cobalt oxidation A point that is dramatically improved as compared with the above is disclosed. Here, this γ-cobalt oxyhydroxide also has a feature that a large amount of alkali cation (K ⁺ or Na ⁺ ) is contained in the crystal. Further, Japanese Patent Application Laid-Open No. H11-147719
In the publication, a lithium hydroxide or lithium ion is fixed inside the crystal of the γ-cobalt oxyhydroxide layer having a cobalt valence higher than 3.0, so that the charge / discharge cycle is performed under a high temperature atmosphere. It is disclosed that the capacity deterioration when repeating is repeated.

The above-mentioned techniques, which have been filed and published in recent years, basically aim to sufficiently perform the cobalt oxidation reaction (which does not proceed satisfactorily under ordinary conditions) occurring at the time of initial charging of the battery sufficiently outside the battery. belongs to. Therefore, it is possible to improve a defect caused by the imperfectness of the conductive network due to the aforementioned cobalt.

On the other hand, the non-sintered nickel electrode has a disadvantage that charging efficiency under a high-temperature atmosphere is low. Usually, at the end of charging of an alkaline storage battery, in addition to the charging reaction (oxidation reaction) from nickel hydroxide to nickel oxyhydroxide, an oxygen generation reaction, which is a side reaction, occurs competitively. In particular, in charging in a high-temperature atmosphere, the oxygen generation overvoltage decreases, so that a large amount of charged electricity is consumed in the oxygen generation reaction. As a result, nickel hydroxide is not sufficiently oxidized to nickel oxyhydroxide, resulting in a decrease in battery capacity.

A number of proposals have been made to solve this problem. For example, Japanese Patent Application Laid-Open No. 5-289
No. 92 discloses that yttrium, indium,
A method of adding at least one compound of antimony, barium, calcium, and beryllium is disclosed. These compounds added to the positive electrode are adsorbed on the surface of the active material nickel hydroxide,
The utilization rate of nickel hydroxide in charging under a high-temperature atmosphere is improved.

Japanese Patent Application Laid-Open No. 10-294109 discloses that an active material powder composed of composite particles in which a coating layer composed of a sodium-containing cobalt compound is formed on the surface of nickel hydroxide particles has an average particle diameter of 0.5. It is disclosed that by using a positive electrode to which a metal yttrium powder and / or a yttrium compound powder of up to 20 μm is added, charging characteristics at high temperatures can be improved. Also, JP-A-11-27
No. 3671 discloses that nickel hydroxide solid solution particles having a coating layer of cobalt oxide having a higher order than 3.0 valence and 0.1 parts by weight of the nickel hydroxide solid solution particles coated with the cobalt oxide. It is disclosed that a non-sintered positive electrode for an alkaline storage battery composed of a mixture of -5.0 parts by weight of metal yttrium powder or yttrium oxide powder has a high utilization rate and excellent over-discharge resistance and the like.

Japanese Patent Application Laid-Open No. Hei 10-21909 discloses that a powder composed of composite particles obtained by coating the surface of nickel hydroxide particles with a eutectic of yttrium hydroxide and cobalt hydroxide is used as a positive electrode active material. This discloses that a high active material utilization rate is exhibited over a long period of time as well as in the initial stage of the charge / discharge cycle. Also, Japanese Unexamined Patent Application Publication No.
Japanese Patent Application Laid-Open No. 260260/1990 discloses that a composite particle obtained by coating at least a part of the surface of a nickel hydroxide particle with a cobalt compound layer containing ytterbium is used as a positive electrode active material, whereby the utilization factor and the temperature in a high-temperature atmosphere are increased. It is disclosed that charging efficiency can be improved.

[0017] Also, JP-A-11-7949 discloses that
Consisting of base particles containing nickel hydroxide, yttrium, scandium, or lanthanoid coating the base particles, or a coating inner layer of a compound thereof, and a coating outer layer of cobalt or a cobalt compound coating the coating inner layer. It is disclosed that by using the composite particles as a positive electrode active material, a high active material utilization rate is exhibited not only when charged at normal temperature but also when charged under a high temperature atmosphere. Further, Japanese Unexamined Patent Application Publication No. 11-7
No. 950 discloses a base particle containing nickel hydroxide, a coating inner layer of cobalt or a cobalt compound coating the base particle, and yttrium, scandium or lanthanoid coating the coating inner layer, or a compound thereof. By using the composite particles comprising the coating outer layer as a positive electrode active material, not only when charged at room temperature, but also when charged under a high temperature atmosphere,
It is disclosed that a high active material utilization rate is exhibited.

[0018]

The above additives have the effect of increasing the oxygen overvoltage and improving the high-temperature charging efficiency, but have little conductivity. Therefore, the effect of imparting electron conductivity to the surface of the nickel hydroxide particles due to the coating of the cobalt oxide is hindered, and the discharge characteristics, particularly the high-rate discharge characteristics, are adversely affected. In particular, when the above-mentioned additive is eutectic in the cobalt oxide coating layer, or when uniformly distributed as the inner layer or the outer layer of the cobalt oxide coating layer, it is excellent when charged under a high temperature atmosphere. Although the active material utilization rate is exhibited, the high-rate discharge characteristics are significantly deteriorated.

The present invention solves the above-mentioned problems, and provides a positive electrode active material for an alkaline storage battery and an alkaline storage battery which are excellent in high-rate discharge characteristics while maintaining excellent high-temperature charging characteristics.

[0020]

In order to solve the above-mentioned problems, a positive electrode active material for an alkaline storage battery according to the present invention comprises 1 to 30% of the surface area of solid solution particles containing nickel hydroxide as a main component.
Is coated with at least one oxide particle selected from yttrium, scandium or lanthanoid, and its outer periphery is coated with a cobalt oxide having an average cobalt valence of more than 3.0. It is characterized by the following.

Since the surface of the nickel hydroxide solid solution particles is partially covered with yttrium, scandium or lanthanoid oxide particles having the effect of increasing the oxygen generation overpotential, the nickel hydroxide solid solution particles and the cobalt on the outer periphery thereof are coated. There is a bond with the oxide coating layer. Therefore, the method of coating the surface of the nickel hydroxide particles with a eutectic of yttrium hydroxide and cobalt hydroxide, or the surface of the nickel hydroxide particles with yttrium, scandium or lanthanoid, or an inner layer made of these compounds The electron conductivity in the active material is improved as compared with the method of coating and further coating with an outer layer made of cobalt or a cobalt compound. Further, since the outermost periphery of the nickel hydroxide solid solution particles is coated with only cobalt oxide, the surface of the nickel hydroxide particles is coated with an inner layer made of cobalt or a cobalt compound, and further, yttrium, scandium or a lanthanoid,
Alternatively, the conductive network between particles and between the particles and the substrate skeleton is not damaged as compared with the method of coating with an outer layer made of such a compound. Therefore, it is possible to provide a positive electrode active material for an alkaline storage battery and an alkaline storage battery that are excellent in high-rate discharge characteristics while maintaining excellent high-temperature charging characteristics.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The positive electrode active material for an alkaline storage battery according to the present invention is characterized in that at least one oxide selected from yttrium, scandium or lanthanoid has a surface area of 1 to 30% of the solid solution particles mainly containing nickel hydroxide. It is characterized in that it is coated with particles and its outer periphery is coated with a cobalt oxide having an average cobalt valence of more than 3.0.

Here, the coverage of at least one oxide particle selected from yttrium, scandium or lanthanoid is as follows: coverage (%) = ((number of oxide particles bound per nickel hydroxide solid solution particle × oxidation) The maximum cross-sectional area of the material particles) / (the surface area of the nickel hydroxide solid solution particles-one particle)) × 100. Here, the number of oxide particles bound per nickel hydroxide solid solution particle is the number of oxide particles bound per nickel hydroxide solid solution particle = (weight of oxide particles in active material / (oxide Volume per particle × True density of oxide) / (Weight of nickel hydroxide solid solution particles in active material / (Volume per nickel hydroxide solid solution particle × True density of nickel hydroxide solid solution particles)) Defined. The oxide particles and the nickel hydroxide solid solution particles are assumed to be spherical in shape and all particles have the average particle diameter, and the cross-sectional area of the particles, the surface area of one particle, and the Was calculated.

Since the surfaces of the nickel hydroxide solid solution particles are partially coated with yttrium, scandium or lanthanoid oxide particles having the effect of increasing the oxygen generation overpotential, the nickel hydroxide solid solution particles and the cobalt on the outer periphery thereof are coated. The presence of the bonding portion with the oxide coating layer improves the electron conductivity in the active material. Further, since the outermost periphery of the nickel hydroxide solid solution particles is covered only with the cobalt oxide, the conductive network connecting the particles and connecting the particles to the substrate skeleton is not damaged. Therefore, a positive electrode active material for an alkaline storage battery and an alkaline storage battery having excellent high-rate discharge characteristics while maintaining excellent high-temperature charging characteristics can be obtained.

In the positive electrode active material, when the coverage of the yttrium, scandium or lanthanoid oxide particles with respect to the surface area of the nickel hydroxide solid solution particles is less than 1%, the oxygen generation overpotential during charging in a high-temperature atmosphere is sufficiently increased. I can't let it. On the other hand, when the coverage is greater than 30%, the effect of increasing the oxygen generation overvoltage is saturated, and the effect of imparting electron conductivity to the surface of the nickel hydroxide particles by the coating layer of cobalt oxide is hindered. Adversely affect

Further, the positive electrode active material for an alkaline storage battery is characterized in that the ratio of the yttrium, scandium or lanthanoid oxide particles to the nickel hydroxide solid solution particles is 0.1 to 3.0% by mass. When the ratio of the oxide particles of yttrium, scandium or lanthanoid is less than 0.1% by mass in the positive electrode active material, the oxygen generation overpotential in charging in a high-temperature atmosphere cannot be sufficiently increased. When the ratio of the oxide particles of yttrium, scandium or lanthanoid is more than 3.0% by mass, the effect of increasing the oxygen overvoltage is saturated, and the electron on the surface of the nickel hydroxide particles by the coating layer of cobalt oxide is saturated. Impedes the effect of imparting conductivity and adversely affects high-rate discharge characteristics.

Further, the solid solution particles containing nickel hydroxide as a main component include cobalt, zinc, cadmium, calcium, manganese, magnesium, aluminum, titanium,
A positive electrode active material for an alkaline storage battery, characterized by containing at least one element selected from yttrium and lanthanoids in a solid solution and / or eutectic state.
By including one or more of the above elements in a solid solution and / or eutectic state in nickel hydroxide, swelling during charging is suppressed, and a positive electrode active material for an alkaline storage battery with less capacity deterioration due to charge / discharge cycles can be obtained. .

[0028] The positive electrode active material for alkaline storage batteries is characterized in that the ratio of the coating layer of the cobalt oxide to the solid solution particles is 5 to 10% by mass. When the ratio of the coating layer is less than 5% by mass, the conductive network becomes insufficient, and the current collection from the active material particles cannot be sufficiently maintained. When the ratio of the coating layer is more than 10% by mass, the amount of nickel hydroxide particles that determines the capacity of the positive electrode is relatively reduced, and a positive electrode having a high energy density cannot be obtained. Most preferably, the ratio of the coating layer is within the above range and the entire surface of the particles is coated in order to maximize the current collecting ability from the nickel hydroxide particles.

Further, the coating layer of the cobalt oxide contains potassium or sodium inside the crystal, and has lithium hydroxide or lithium ions immobilized thereon. It is. By forming a coating layer of the above cobalt oxide,
It is possible to suppress capacity deterioration when a charge / discharge cycle is repeated in a high temperature atmosphere.

As a non-sintered positive electrode suitable for an alkaline storage battery to which the positive electrode active material of the present invention is applied, a paste type positive electrode obtained by applying a paste containing the active material to a conductive core and drying the paste is exemplified. Can be Specific examples of the conductive core at this time include a nickel foam, a felt-like porous metal fiber, and a punching metal.

Specific examples of a suitable alkaline storage battery using the positive electrode active material of the present invention include a nickel-hydrogen storage battery, a nickel-cadmium storage battery, and a nickel-zinc storage battery.

[0032]

Embodiments of the present invention will be described below in detail.

Example 1 Nickel hydroxide solid solution particles as a positive electrode active material were synthesized by using the following well-known technique. That is, sodium hydroxide is gradually added dropwise to an aqueous solution containing nickel sulfate as a main component and a predetermined amount of cobalt sulfate and zinc sulfate while adjusting the solution pH with aqueous ammonia to form spherical nickel hydroxide solid solution particles. The method of precipitating was used. The precipitated nickel hydroxide solid solution particles were washed with water and dried to obtain active material particles. The average particle size of the nickel hydroxide solid solution particles was 10 μm.

Next, 100 parts by weight of the nickel hydroxide solid solution particles thus obtained was added to Y ₂ having an average particle size of 0.2 μm.
After adding 0.5 parts by weight of O ₃ particles, the mixture was subjected to a mechanochemical reaction (mechanofusion method) by a compression-milling pulverizer, and Y ₂ O ₃ particles were added to the surface of the nickel hydroxide solid solution particles. Was dispersed to prepare Y oxide-dispersed nickel hydroxide solid solution particles. In this case, the coverage of the Y ₂ O ₃ particles with respect to the surface area of the nickel hydroxide solid solution particles is 4.
8%. Further, it was confirmed from the yttrium characteristic X-ray image that yttrium was partially present on the surface of the nickel hydroxide solid solution particles.

The yttrium thus obtained (hereinafter referred to as Y
The oxide-dispersed nickel hydroxide solid solution particles were put into an aqueous solution of cobalt sulfate, and an aqueous solution of sodium hydroxide was gradually added thereto. The mixture was stirred at 35 ° C. while maintaining the pH at 12 to maintain the solid solution particle surface. Then, cobalt hydroxide was precipitated to prepare nickel hydroxide-coated nickel oxide-dispersed nickel hydroxide solid solution particles. Here, the coating amount of cobalt hydroxide was adjusted so that the weight ratio of the coating layer to the nickel hydroxide solid solution particles was 7.0% by mass. The produced cobalt hydroxide-coated Y oxide-dispersed nickel hydroxide solid solution particles were washed with water and then dried in vacuum.

Subsequently, the cobalt hydroxide-coated Y oxide-dispersed nickel hydroxide solid solution particles are impregnated with an appropriate amount of a 45% by mass aqueous solution of potassium hydroxide, and then put into a drying apparatus having a microwave heating function. To bring the particles to complete drying with oxygen. By this operation, the cobalt hydroxide coating layer on the surface of the particles was oxidized to a higher state exceeding 3.0 valence, and turned to blue. This was sufficiently washed with water and vacuum dried to obtain cobalt oxide-treated Y oxide-dispersed active material particles (hereinafter referred to as active material A of the present invention).

Further, the nickel hydroxide solid solution particles are put into an aqueous solution of yttrium nitrate, an aqueous solution of sodium hydroxide is gradually added thereto, and stirring is continued while adjusting the pH at 11 at 35 ° C. to maintain the surface of the solid solution particles. Then, yttrium hydroxide was precipitated to prepare solid solution particles of nickel oxide-coated nickel hydroxide. Here, the coating amount of yttrium hydroxide was adjusted so that the weight ratio of the coating layer to the nickel hydroxide solid solution particles was 0.5% by mass in terms of Y ₂ O ₃ . The produced Y oxide-coated nickel hydroxide solid solution particles were washed with water and then dried at 80 ° C.

The thus obtained Y oxide-coated nickel hydroxide solid solution particles are put into an aqueous solution of cobalt sulfate, and an aqueous solution of sodium hydroxide is gradually added thereto.
The stirring was continued while maintaining such that the temperature was maintained to deposit cobalt hydroxide on the surface of the Y oxide coating layer, thereby producing cobalt oxide-coated Y oxide-coated nickel hydroxide solid solution particles. Here, as for the coating amount of cobalt hydroxide, the ratio of the weight of the coating layer to the solid solution particles of nickel hydroxide is 7.
It was adjusted to be 0% by mass. The prepared cobalt hydroxide-coated Y oxide-coated nickel hydroxide solid solution particles were washed with water and then vacuum-dried.

Subsequently, an appropriate amount of a 45% by mass aqueous solution of potassium hydroxide is impregnated into the cobalt hydroxide-coated Y oxide-coated nickel hydroxide solid solution particles, and this is put into a drying apparatus having a microwave heating function. To bring the particles to complete drying with oxygen. By this operation, the cobalt hydroxide coating layer on the surface of the particles was oxidized to a higher state exceeding 3.0 valence, and turned to blue. This was sufficiently washed with water and dried under vacuum to obtain Co-oxidized Y oxide-coated active material particles (hereinafter referred to as comparative active material B).

Further, the nickel hydroxide solid solution particles are charged into an aqueous solution of cobalt sulfate, an aqueous solution of sodium hydroxide is gradually added, and stirring is continued while adjusting the pH at 12 at 35 ° C. to maintain a pH of 12. Cobalt hydroxide was deposited on the surface of the solid solution particles to prepare cobalt hydroxide-coated nickel hydroxide solid solution particles. Here, the coating amount of cobalt hydroxide was adjusted so that the weight ratio of the coating layer to the nickel hydroxide solid solution particles was 7.0% by mass. The prepared cobalt hydroxide-coated nickel hydroxide solid solution particles were washed with water and then dried in vacuum.

Subsequently, the cobalt hydroxide-coated nickel hydroxide solid solution particles are impregnated with an appropriate amount of a 45% by mass aqueous solution of potassium hydroxide, and the mixture is introduced into a drying apparatus having a microwave heating function and heated. The particles were led to complete drying while sending oxygen. By this operation, the cobalt hydroxide coating layer on the surface of the particles was oxidized to a higher state exceeding 3.0 valence, and turned to blue. This was sufficiently washed with water and dried under vacuum to obtain Co-oxidized active material particles.

The Co-oxidized active material particles thus obtained are put into an yttrium nitrate aqueous solution, an aqueous sodium hydroxide solution is gradually added, and stirring is continued while adjusting the pH at 11 at 35 ° C. while maintaining the pH at 11. Yttrium hydroxide is deposited on the surface of the cobalt oxide coating layer to form a Y oxide coating C
o Oxidation-treated active material particles were produced. Here, the coating amount of yttrium hydroxide was adjusted so that the weight ratio of the coating layer to the nickel hydroxide solid solution particles was 0.5% by mass in terms of Y ₂ O ₃ . The produced Y oxide-coated Co oxidized active material particles were washed with water and then dried at 80 ° C. (hereinafter referred to as comparative active material C).

Further, the nickel hydroxide solid solution particles were charged into a mixed aqueous solution of cobalt nitrate and yttrium nitrate, and an aqueous sodium hydroxide solution was gradually added thereto.
Stirring is continued while adjusting to maintain H = 12 to precipitate a mixed crystal of cobalt hydroxide and yttrium hydroxide on the surface of the nickel hydroxide solid solution particles, thereby forming a Y mixed crystal cobalt hydroxide-coated nickel hydroxide solid solution particle. Produced. Here, the coating amount of cobalt hydroxide was adjusted so that the weight ratio of the coating layer to the nickel hydroxide solid solution particles was 7.0% by mass. The coating amount of yttrium hydroxide was adjusted so that the weight ratio of the coating layer to the nickel hydroxide solid solution particles was 0.5% by mass in terms of Y ₂ O ₃ . The produced Y mixed crystal cobalt hydroxide-coated nickel hydroxide solid solution particles were washed with water and then dried in vacuum.

Subsequently, the Y mixed crystal cobalt hydroxide-coated nickel hydroxide solid solution particles are impregnated with an appropriate amount of a 45% by mass aqueous solution of potassium hydroxide, and put into a drying apparatus having a microwave heating function. Heating and sending oxygen led the particles to complete drying. By this operation, the cobalt hydroxide coating layer on the surface of the particles was oxidized to a higher state exceeding 3.0 valence, and turned to blue. This was sufficiently washed with water and dried in vacuum to obtain Y mixed crystal Co oxidized active material particles (hereinafter referred to as comparative active material D).

Further, the solid solution of nickel hydroxide was put into an aqueous solution of cobalt sulfate, an aqueous solution of sodium hydroxide was gradually added, and stirring was continued while adjusting the pH at 12 at 35 ° C. while maintaining the pH at 12. Cobalt hydroxide was deposited on the surface of the solid solution particles to prepare cobalt hydroxide-coated nickel hydroxide solid solution particles. Here, the coating amount of cobalt hydroxide was adjusted so that the weight ratio of the coating layer to the nickel hydroxide solid solution particles was 7.0% by mass. The prepared cobalt hydroxide-coated nickel hydroxide solid solution particles were washed with water and then dried in vacuum.

Subsequently, the cobalt hydroxide-coated nickel hydroxide solid solution particles are impregnated with an appropriate amount of a 45% by mass aqueous solution of potassium hydroxide, and the mixture is introduced into a drying apparatus having a microwave heating function and heated. The particles were led to complete drying while sending oxygen. By this operation, the cobalt hydroxide coating layer on the surface of the particles was oxidized to a higher state exceeding 3.0 valence, and turned to blue. This was sufficiently washed with water and vacuum dried to obtain Co-oxidized active material particles (hereinafter referred to as comparative active material E).

Next, the active material A of the present invention thus obtained,
To 100 parts by weight of the comparative active materials B, C and D, 0.1 part by weight of carboxymethyl cellulose (CMC) as a thickener and 0.2 part by weight of polytetrafluoroethylene (PTFE) as a binder were used. Of pure water was added and mixed and dispersed to obtain an active material slurry. This active material slurry was filled in a foamed nickel porous substrate having a thickness of 1.4 mm, dried in a drier at 80 ° C., and then rolled to about 0.7 mm by a roll press, and further reduced to a predetermined size. By cutting, a nickel positive electrode having a theoretical capacity of 1200 mAh based on a one-electron reaction of Ni was obtained. This positive electrode and a negative electrode mainly composed of a hydrogen storage alloy, a polypropylene nonwoven fabric separator subjected to a hydrophilic treatment, a potassium hydroxide concentration of 7.0 N, and a lithium hydroxide concentration of 1.
Using a mixed alkaline electrolyte of 0 normality and a known method, an AA size nickel alloy having a nominal capacity of 1200 mAh was used.
Hydrogen storage batteries were produced (hereinafter, these batteries corresponding to the active material A of the present invention and the comparative active materials B, C, and D are referred to as a battery A of the present invention and comparative batteries B, C, and D, respectively).

A nickel-hydrogen storage battery was manufactured in the same manner as above except that 0.5 parts by weight of Y ₂ O ₃ having an average particle size of 0.2 μm was added to 100 parts by weight of the comparative active material E. (Hereinafter referred to as Comparative Battery E).

Further, except that the comparative active material E was used, and that Y ₂ O ₃ was not added, the same procedure as above was carried out to obtain a nickel alloy.
A hydrogen storage battery was produced (hereinafter referred to as a comparative battery F).

These six types of batteries A, B, C, D, E, F
At a constant temperature of 20 ° C. and a charge of 120 mA at 1
After 5 hours, discharge was performed at 240 mA at a cutoff voltage of 0.8 V, and this charge / discharge operation was repeated 5 times.

Next, charging was performed at a constant temperature of 20 ° C. for 120 m.
A for 15 hours, and after a pause of 2 hours, discharge was performed at a constant temperature of 20 ° C. at 240 mA to a final voltage of 0.8 V, and the amount of discharge electricity at this time was measured and defined as discharge capacity.

Further, charging at a constant temperature of 50 ° C. for 120 m
A for 15 hours, and after a pause of 2 hours, discharge was performed at a constant temperature of 20 ° C. at 240 mA to a final voltage of 0.8 V, and the amount of discharge electricity at this time was measured and defined as discharge capacity.

Further, charging at a constant temperature of 20 ° C. for 120
After a pause of 2 hours, the battery was discharged at a constant temperature of 20 ° C. and a final voltage of 0.8 V at 3600 mA. The amount of discharged electricity at this time was measured and defined as a discharge capacity.

Table 1 shows the results of the charge / discharge test as the utilization factor and the charging efficiency at 50 ° C. The utilization rate is defined as the theoretical capacity based on the one-electron reaction of Ni as a reference, and is defined as utilization rate (%) = discharge capacity / theoretical capacity × 100 as an index indicating how much discharge has occurred relative to the theoretical capacity. did. Here, the utilization rate is used for the discharge capacity, the utilization rate is used for the discharge capacity, and the utilization rate is used for the discharge capacity. The 50 ° C. charge efficiency was defined as 50 ° C. charge efficiency (%) = discharge capacity / discharge capacity as an index indicating how much charge was performed during 20 ° C. charge.

[0055]

[Table 1]

The battery A of the present invention has a charging efficiency of 50% at 50 ° C., whereas the comparative battery B has a charging efficiency of 81% and the comparative battery C has a charging efficiency of 8%.
0%, Comparative battery D 81%, Comparative battery E 76%, Comparative battery F 67%, and improvement of high-temperature charging efficiency was confirmed in batteries A, B, C, D, and E to which yttrium was added. it can. In particular, batteries A, B, C, in which yttrium exists near or in the cobalt oxide coating layer,
D shows excellent high-temperature charging efficiency. This phenomenon is considered to be due to the fact that the dispersibility of yttrium is high, and this has effectively acted on the increase of the oxygen overvoltage.

The utilization rate at the discharge of 3600 mA was 74% for the battery A of the present invention and 6% for the comparative battery B.
4%, Comparative Battery C was 65%, Comparative Battery D was 64%, Comparative Battery E was 69%, Comparative Battery F was 74%, indicating that Battery A of the present invention was also excellent in high-rate discharge characteristics. . This result indicates that since the yttrium oxide particles are partially coated on the surface of the nickel hydroxide solid solution particles, the bonding portion between the nickel hydroxide solid solution particles and the cobalt oxide coating layer on the outer periphery thereof exists, Because the electron conductivity in the material is not impaired, and because the outermost periphery of the active material particles is coated only with the cobalt oxide, the conductive network connecting the particles and between the particles and the substrate skeleton is not impaired. Conceivable.

Example 2 Y ₂ O _{3 having} an average particle size of 0.2 μm
Particles with a coverage of 0.5, 1, 5, 10, 3 respectively
Co-oxidized Y-oxide dispersed active material particles were produced in the same manner as in Example 1 except that the coating was performed so as to be 0 and 50%, and a nickel-hydrogen storage battery was produced using these. For these batteries, the same charge / discharge evaluation as in Example 1 was performed, and the charging efficiency at 50 ° C. and the high rate discharge characteristics were measured.
FIG. 1 shows the evaluation results of the charging efficiency at 50 ° C., and FIG. 2 shows the evaluation results of the high-rate discharge characteristics.

FIG. 1 shows that the coverage of the Y ₂ O ₃ particles was 0.5%.
In the case of, it can be seen that almost no improvement in the high-temperature charging efficiency can be confirmed. In addition, when the Y ₂ O ₃ particles are coated at 1% or more, the improvement of the high-temperature charging efficiency can be confirmed. However, when the coating is performed at more than 30%, the effect is saturated, and no further effect is obtained. It could be confirmed. Furthermore, it can be seen from FIG. 2 that when more than 30% of the Y ₂ O ₃ particles are coated, the high-rate discharge characteristics are adversely affected. It is considered that a large amount of Y ₂ O ₃ exists between the cobalt oxide coating layer and the surface of the nickel hydroxide particles, so that the effect of imparting electron conductivity to the surface of the nickel hydroxide particles by the coating layer of the cobalt oxide was hindered. Can be From the above results, it is clear that when the Y ₂ O ₃ particles are covered with 1 to 30% of the surface area of the nickel hydroxide solid solution particles, the high-temperature charge characteristics and the high-rate discharge characteristics are excellent.

Example 3 Y ₂ O _{3 having} an average particle size of 0.3 μm
Particles are respectively 0.05, 0.1, 0.5, 1.0,
Co-oxidized Y oxide dispersed active material particles were prepared in the same manner as in Example 1 except that 3.0 and 5.0 parts by weight were added, and a nickel-hydrogen storage battery was prepared using these particles. For these batteries, the same charge / discharge evaluation as in Example 1 was performed, and the charging efficiency at 50 ° C. and the high rate discharge characteristics were measured.
FIG. 3 shows the evaluation results of the charging efficiency at 50 ° C., and FIG. 4 shows the evaluation results of the high-rate discharge characteristics.

FIG. 3 shows that the addition amount of Y ₂ O ₃ particles was 0.05
In the case of parts by weight, it can be seen that the improvement in high-temperature charging efficiency can hardly be confirmed. In addition, when Y ₂ O ₃ particles are added in an amount of 0.1 part by weight or more, improvement in high-temperature charging efficiency can be confirmed.
Even if more than 3.0 parts by weight is added, the effect is saturated,
It was confirmed that no further effect was obtained. Furthermore, FIG. 4 shows that the addition of more than 3.0 parts by weight of Y ₂ O ₃ particles has a bad influence on the high-rate discharge characteristics. It is considered that a large amount of Y ₂ O ₃ exists between the cobalt oxide coating layer and the surface of the nickel hydroxide particles, so that the effect of imparting electron conductivity to the surface of the nickel hydroxide particles by the coating layer of the cobalt oxide was hindered. Can be based on the above results,
It is clear that when Y ₂ O ₃ particles are added in an amount of 0.1 to 3.0% by mass, the high-temperature charge characteristics and the high-rate discharge characteristics are also excellent.

In this example, the coating layer was formed by using a chemical reaction in an aqueous solution when coating with cobalt hydroxide. However, the coating conditions and the like at this time are not limited to those described here. It is not done. A method of mixing Y oxide-dispersed nickel hydroxide solid solution particles and cobalt hydroxide powder and coating the particle surface with cobalt hydroxide using a shearing force or an impact force during mechanical mixing (mechanical mixing method) or the like. Thus, the positive electrode of the present invention can be produced also as a solid solution particle of nickel hydroxide dispersed in a cobalt oxide-coated Y oxide.

In oxidizing the cobalt hydroxide-coated Y oxide-dispersed nickel hydroxide solid solution particles, a high-concentration aqueous solution of sodium hydroxide was used, but the same effect was obtained even when a high-concentration aqueous solution of potassium hydroxide was used. can get. As a heating method for oxidizing the alkali-moistened cobalt hydroxide-coated Y oxide-dispersed nickel hydroxide solid solution particles, a method of heating while feeding oxygen in a dryer having a microwave heating function was used, but is not limited thereto. Not something. Similar effects can be obtained even when cobalt hydroxide-coated nickel hydroxide solid solution particles having lithium hydroxide or lithium ions immobilized inside the crystal of the cobalt oxide coating layer are used.

Here, the ratio of the cobalt oxide coating layer is preferably 5 to 10% by mass. When the ratio of the coating layer is less than 5% by mass, the conductive network becomes insufficient, and the current collection from the active material particles cannot be sufficiently maintained.
When the ratio of the coating layer is more than 10% by mass, the amount of nickel hydroxide particles that determines the capacity of the positive electrode is relatively reduced, and a positive electrode having a high energy density cannot be obtained. Most preferably, the ratio of the coating layer is within the above range and the entire surface of the particles is coated in order to maximize the current collecting ability from the nickel hydroxide particles.

In the present embodiment, solid solution particles of nickel, cobalt and zinc were used for the preparation of solid solution particles of nickel hydroxide, but the elements of the solid solution species are not limited to those described here. Similar effects can be obtained in all nickel hydroxide particles containing at least one element selected from cobalt, zinc, cadmium, calcium, manganese, magnesium, aluminum, titanium, yttrium and lanthanoids in a solid solution and / or eutectic state. Can be

Further, the effect in the present embodiment is not limited to the case where Y ₂ O ₃ particles are added, and the same effect can be obtained even when scandium or lanthanoid oxide particles are added. It was confirmed.

[0067]

As described above, by using the positive electrode active material of the present invention, a positive electrode active material for an alkaline storage battery and an alkaline storage battery having excellent high-temperature discharge characteristics and excellent high-rate discharge characteristics can be obtained. Can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing charging efficiency when each battery used in Example 2 is charged at 50 ° C.

FIG. 2 is a diagram showing the utilization rate of each battery used in Example 2 at 3600 mA discharge.

FIG. 3 is a diagram showing charging efficiency when each battery used in Example 3 is charged at 50 ° C.

FIG. 4 is a diagram showing the utilization rate of each battery used in Example 3 at a discharge of 3600 mA.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yoichi Izumi 1006 Kazuma Kadoma, Osaka Pref. Matsushita Electric Industrial Co., Ltd. Terms (reference) 5H028 AA06 BB03 BB05 EE05 EE10 HH00 HH01 5H050 AA05 BA11 CA04 CB13 CB14 CB16 DA09 EA12 FA17 FA18 FA19 GA02 GA22 HA00 HA01 HA07 HA13

Claims (6)

[Claims] 1. A solid solution particle comprising nickel hydroxide as a main component, wherein 1 to 30% of the surface area of the solid solution particle is coated with at least one oxide particle selected from yttrium, scandium or lanthanoid. ,
A positive electrode active material for an alkaline storage battery, wherein the outer periphery is coated with a cobalt oxide having an average cobalt valence of more than 3.0. 2. The positive electrode active material for an alkaline storage battery according to claim 1, wherein a ratio of the yttrium, scandium, or lanthanoid oxide particles to the solid solution particles is 0.1 to 3.0% by mass. 3. The method according to claim 1, wherein the solid solution particles contain at least one element selected from the group consisting of cobalt, zinc, cadmium, calcium, manganese, magnesium, aluminum, titanium, yttrium, and lanthanoids in a solid solution and / or eutectic state. The positive electrode active material for an alkaline storage battery according to claim 1 or 2, wherein: 4. The positive electrode active material for an alkaline storage battery according to claim 1, wherein a ratio of the coating layer of the cobalt oxide to the solid solution particles is 5 to 10% by mass. material. 5. The coating layer of the cobalt oxide contains potassium or sodium inside the crystal thereof.
The positive electrode active material for an alkaline storage battery according to any one of claims 1 to 4, wherein lithium hydroxide or lithium ions are immobilized. 6. A positive electrode comprising the positive electrode active material according to claim 1 as a main component, a negative electrode comprising a hydrogen storage alloy or cadmium oxide as a main component, a separator, an alkaline electrolyte, and the like. Alkaline storage battery consisting of a battery case that houses